During science lab, some students added small pieces of magnesium ribbon to 10 ml of hydrochloric acid. they noticed that bubbles formed, the test tube got hot, and the magnesium disappeared.
which is a sign that a chemical reaction has taken place in this experiment?
a) change in odor
b) change in color
c) release of heat energy
d) disappearance of magnesium

C) release of heat energy

Explanation: A chemical change is a change which is accompanied by a change in chemical composition of the atoms.

Chemical changes are accompanied by:

a) Change in color

b) Absorption or release of heat

c) formation of precipitates

d) production of gas.

Here no change in color is there, but is given that the tube gets hot, that means the energy has been released.

i believe the answer is a.